Biased pulse DC reactive sputtering of oxide films

ABSTRACT

A biased pulse DC reactor for sputtering of oxide films is presented. The biased pulse DC reactor couples pulsed DC at a particular frequency to the target through a filter which filters out the effects of a bias power applied to the substrate, protecting the pulsed DC power supply. Films deposited utilizing the reactor have controllable material properties such as the index of refraction. Optical components such as waveguide amplifiers and multiplexers can be fabricated using processes performed on a reactor according to the present invention.

This is a division of application Ser. No. 10/101,863, filed Mar. 16,2002, which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to deposition of oxide and oxynitridefilms and, in particular, to deposition of oxide and oxynitride films bypulsed DC reactive sputtering.

2. Discussion of Related Art

Deposition of insulating materials and especially optical materials istechnologically important in several areas including production ofoptical devices and production of semiconductor devices. Insemiconductor devices, doped alumina silicates can be utilized as highdielectric insulators.

The increasing prevalence of fiber optic communications systems hascreated an unprecedented demand for devices for processing opticalsignals. Planar devices such as optical waveguides, couplers, splitters,and amplifiers, fabricated on planar substrates, like those commonlyused for integrated circuits, and configured to receive and processsignals from optical fibers are highly desirable. Such devices holdpromise for integrated optical and electronic signal processing on asingle semiconductor-like substance.

The basic design of planar optical waveguides and amplifiers is wellknown, as described, for example, in U.S. Pat. Nos. 5,119,460 and5,563,979 to Bruce et al., U.S. Pat. No. 5,613,995 to Bhandarkar et al.,U.S. Pat. No. 5,900,057 to Buchal et al., and U.S. Pat. No. 5,107,538 toBenton et al., to cite only a few. These devices, very generally,include a core region, typically bar shaped, of a certain refractiveindex surrounded by a cladding region of a lower refractive index. Inthe case of an optical amplifier, the core region includes a certainconcentration of a dopant, typically a rare earth ion such as an erbiumor praseodymium ion which, when pumped by a laser, fluoresces, forexample, in the 1550 nm and 1300 nm wavelength ranges used for opticalcommunication, to amplify the optical signal passing through the core.

As described, for example in the patents by Bruce et al., Bhandarkar etal, and Buchal et al., planar optical devices may be fabricated byprocess sequences including forming a layer of cladding material on asubstrate; forming a layer of core material on the layer of claddingmater; patterning the core layer using a photolighotgraphic mask and anetching process to form a core ridge; and covering the core ridge withan upper cladding layer.

The performance of these planar optical devices depends sensitively onthe value and uniformity of the refractive index of the core region andof the cladding region, and particularly on the difference in refractiveindex, Δn, between the regions. Particularly for passive devices such aswaveguides, couplers, and splitters, Δn should be carefully controlled,for example to values within about 1%, and the refractive index of bothcore and cladding need to be highly uniform, for some applications atthe fewer than parts per thousand level. In the case of doped materialsforming the core region of planar optical amplifiers, it is importantthat the dopant be uniformly distributed so as to avoid non-radiativequenching or radiative quenching, for example by upconversion. Therefractive index and other desirable properties of the core and claddingregions, such as physical and chemical uniformity, low stress, and highdensity, depend, of course, on the choice of materials for the devicesand on the processes by which they are fabricated.

Because of their optical properties, silica and refractory oxides suchas Al₂O₃, are good candidate materials for planar optical devices.Further, these oxides serve as suitable hosts for are earth dopants usedin optical amplifiers. A common material choice is so-called lowtemperature glasses, doped with alkali metals, boron, or phosphorous,which have the advantage of requiring lower processing temperatures. Inaddition, dopants are used to modify the refractive index. Methods suchas flame hydrolysis, ion exchange for introducing alkali ions inglasses, sputtering, and various chemical vapor deposition processes(CVD) have been used to form films of doped glasses. However, dopantssuch as phosphorous and boron are hygroscopic, and alkalis areundesirable for integration with electronic devices. Control ofuniformity of doping in CVD processes can be difficult and CVD depositedfilms can have structural defects leading to scattering losses when usedto guide light. In addition, doped low temperature glasses may requirefurther processing after deposition. A method for eliminating bubbles inthin films of sodium-boro-silicate glass by high temperature sinteringis described, for example, in the '995 patent to Bhandarkar et al.

Typically, RF sputtering has been utilized for deposition of oxidedielectric films. However, RF sputtering utilizes ceramic targets whichare typically formed of multiple smaller tiles. Since the tiles can notbe made very large, there may be a large problem of arcing between tilesand therefore contamination of the deposited film due to this arcing.Further, the reactors required for RF sputtering tend to be rathercomplicated. In particular, the engineering of low capacitance efficientRF power distribution to the cathode is difficult in RF systems. Routingof low capacitance forward and return power into a vacuum vessel of thereaction chamber often exposes the power path in such a way that diffuseplasma discharge is allowed under some conditions of impedance tuning ofthe matching networks.

Therefore, there is a need for new methods of depositing oxide andoxynitride films and for forming planar optical devices.

SUMMARY

In accordance with the present invention, a sputtering reactor apparatusfor depositing oxide and oxynitride films is presented. Further, methodsfor depositing oxide and oxynitride films for optical waveguide devicesare also presented. A sputtering reactor according to the presentinvention includes a pulsed DC power supply coupled through a filter toa target and a substrate electrode coupled to an RF power supply. Asubstrate mounted on the substrate electrode is therefore supplied witha bias from the RF power supply.

The target can be a metallic target made of a material to be depositedon the substrate. In some embodiments, the metallic target is formedfrom Al, Si and various rare-earth ions. A target with an erbiumconcentration, for example, can be utilized to deposit a film that canbe formed into a waveguide optical amplifier.

A substrate can be any material and, in some embodiments, is a siliconwafer. In some embodiments, RF power can be supplied to the wafer. Insome embodiments, the wafer and the electrode can be separated by aninsulating glass.

In some embodiments, up to about 10 kW of pulsed DC power at a frequencyof between about 40 kHz and 350 kHz and a reverse pulse time of up toabout 5 μs is supplied to the target. The wafer can be biased with up toabout several hundred watts of RF power. The temperature of thesubstrate can be controlled to within about 10° C. and can vary fromabout −50° C. to several hundred degrees C. Process gasses can be fedinto the reaction chamber of the reactor apparatus. In some embodiments,the process gasses can include combinations of Ar, N₂, O₂, C₂F₆, CO₂, COand other process gasses.

Several material properties of the deposited layer can be modified byadjusting the composition of the target, the composition and flowrate ofthe process gasses, the power supplied to the target and the substrate,and the temperature of the substrate. For example, the index ofrefraction of the deposited layer depends on deposition parameters.Further, in some embodiments stress can be relieved on the substrate bydepositing a thin film of material on a back side of the wafer. Filmsdeposited according to the present invention can be utilized to formoptical waveguide devices such as multiplexers and rare-earth dopedamplifiers.

These and other embodiments, along with examples of material layersdeposited according to the present invention, are further describedbelow with respect to the following figures.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B show a pulsed DC sputtering reactor according to thepresent invention.

FIG. 2 shows a planar view of target utilized in a reactor as shown inFIGS. 1A and 1B.

FIG. 3 shows a cross-section view of an example target utilized in areactor as shown in FIG. 1A and 1B.

FIG. 4 shows a flow chart of an embodiment of a process for depositing afilm on a substrate according to the present invention.

FIG. 5 shows a hysterises curve of target voltage versus oxygen flowrates for an example target in an embodiment of a reactor according tothe present invention.

FIG. 6 shows a photo-luminescence and lifetimes of a film deposited in aprocess according to the present invention as a function of afterdeposition anneal temperature.

FIG. 7 shows the relationship between the index of refraction of a filmas a function of deposited oxide layers according to the presentinvention and due to oxide build-up on the target.

FIG. 8 shows a graph of the index of refraction of a film depositedaccording to the present invention as a function of the aluminum contentin a composite Al/Si target.

FIG. 9 shows a graph of typical indices of refraction of material layersdeposited according to the present invention.

FIG. 10 shows a table of indices of refraction for a silica layerdeposited according to the present invention as a function of differentprocess parameters.

FIG. 11 shows the refractive indices as a function of O₂/Ar ratioutilized in an Alumina process according to the present invention.

FIG. 12 shows the refractive indices as a function of DC pulsed powerfrequency for an Alumina layer deposited according to the presentinvention.

FIG. 13 shows variation in the refractive index over time duringrepeated depositions from a single target.

FIG. 14 shows variation in refractive index over time for repeateddepositions from a target of another material layer according to thepresent invention.

FIG. 15 shows the variation refractive index over time for repeateddepositions from a target of another material layer according to thepresent invention.

FIG. 16A through 16D shows a TEM film deposited according to the presentinvention.

FIG. 17 shows the transparency of a film deposited according to thepresent invention.

FIG. 18 shows an uppercladding layer deposited according to the presentinvention over a multiple-waveguide structure such that the depositedlayer is substantially planarized.

FIG. 19 illustrates the deposition of a film over a waveguide structure.

FIGS. 20 and 21 illustrate different etch and deposition rates fordeposition of films as a function of the surface angle of the film.

FIG. 22 illustrates calculation of the planarization time for aparticular deposition process.

FIGS. 23 through 25 through illustrate adjustment of process parametersin order to achieve planarization of a film deposited over a waveguidestructure according to the present invention.

FIG. 26 shows the gain characteristics of an erbium doped waveguideamplifier formed of films depositions according to the presentinvention.

FIG. 27 shows gain, insertion loss of a waveguide with an active coredeposited according to the present invention.

FIG. 28 shows up-conversion constants, and lifetimes of the active corelayer of FIG. 27 deposited according to the present invention.

FIG. 29 shows drift in the index of refraction with subsequentdepositions for films deposited from a target according to the presentinvention.

FIG. 30 shows drift in the photoluminescence with subsequent depositionsaccording to the present invention.

FIG. 31 shows drift in the excited state lifetime with subsequentdepositions according to the present invention.

FIG. 32 shows stabilization of the index of refraction in subsequentdepositions.

FIG. 33 shows the index of refraction of a film formed from a puresilicon target as a function of the ratio of O₂/N₂ in the process gas.

In the figures, elements having the same designation have the same orsimilar function.

DETAILED DESCRIPTION

Reactive DC magnetron sputtering of nitrides and carbides is a widelypracticed technique, but the reactive dc magnetron sputtering ofnonconducting oxides is done rarely. Films such as aluminum oxide arealmost impossible to deposit by conventional reactive DC magnetronsputtering due to rapid formation of insulating oxide layers on thetarget surface. The insulating surfaces charges up and result in arcingduring process. This arcing can damage the power supply, produceparticles and degrade the properties of deposited oxide films.

RF sputtering of oxide films is discussed in application Ser. No.09/903,050 (the '050 application) (now U.S. Pat. No. 6,506,289) byDemaray et al, entitled “Planar Optical Devices and Methods for TheirManufacture,” assigned to the same assignee as is the present invention,herein incorporated by reference in its entirety. Further, targets thatcan be utilized in a reactor according to the present invention arediscussed in U.S. application Ser. No. 10/101,341 (the '341application), filed concurrently with the present disclosure, assignedto the same assignee as is the present invention, herein incorporated byreference in its entirety. A gain-flattened amplifier formed of filmsdeposited according to the present invention are described in U.S.application Ser. No. 10/101,493 (the '493 application), filedconcurrently with the present disclosure, assigned to the same assigneeas is the present invention, herein incorporated by reference in itsentirety. Further, a mode size converter formed with films depositedaccording to the present invention is described in U.S. application Ser.No. 10/101,492 (the '492 application) (now U.S. Pat. No. 6,884,327),filed concurrently with the present disclosure, assigned to the sameassignee as is the present invention, herein incorporated by referencein its entirety.

FIG. 1A shows a schematic of a reactor apparatus 10 for sputtering ofmaterial from a target 12 according to the present invention. In someembodiments, apparatus 10 may, for example, be adapted from an AKT-1600PVD (400×500 mm substrate size) system from Applied Komatsu or anAKT-4300 (600×720 mm substrate size) system from Applied Komatsu, SantaClara, Calif. The AKT-1600 reactor, for example, has three depositionchambers connected by a vacuum transport chamber. These Komatsu reactorscan be modified such that pulsed DC power is supplied to the target andRF power is supplied to the substrate during deposition of a materialfilm.

Apparatus 10 includes a target 12 which is electrically coupled througha filter 15 to a pulsed DC power supply 14. In some embodiments, target12 is a wide area sputter source target, which provides material to bedeposited on substrate 16. Substrate 16 is positioned parallel to andopposite target 12. Target 12 functions as a cathode when power isapplied to it and is equivalently termed a cathode. Application of powerto target 12 creates a plasma 53. Substrate 16 is capacitively coupledto an electrode 17 through an insulator 54. Electrode 17 can be coupledto an RF power supply 18. Magnet 20 is scanned across the top of target12.

For pulsed reactive dc magnetron sputtering, as performed by apparatus10, the polarity of the power supplied to target 12 by power supply 14oscillates between negative and positive potentials. During the positiveperiod, the insulating layer on the surface of target 12 is dischargedand arcing is prevented. To obtain arc free deposition, the pulsingfrequency exceeds a critical frequency that depend on target material,cathode current and reverse time. High quality oxide films can be madeusing reactive pulse DC magnetron sputtering in apparatus 10.

Pulsed DC power supply 14 can be any pulsed DC power supply, for examplean AE Pinnacle plus 10K by Advanced-Energy, Inc. With this examplesupply, up to 10 kW of pulsed DC power can be supplied at a frequency ofbetween 0 and 350 KHz. The reverse voltage is 10% of the negative targetvoltage. Utilization of other power supplies will lead to differentpower characteristics, frequency characteristics and reverse voltagepercentages. The reverse time on this embodiment of power supply 14 canbe adjusted between 0 and 5 μs.

Filter 15 prevents the bias power from power supply 18 from couplinginto pulsed DC power supply 14. In some embodiments, power supply 18 isa 2 MHz RF power supply, for example can be a Nova-25 power supply madeby ENI, Colorado Springs, Colo.

Therefore, filter 15 is a 2 MHz band rejection filter. In someembodiments, the band width of the filter can be approximately 100 kHz.Filter 15, therefore, prevents the 2 MHz power from the bias tosubstrate 16 from damaging power supply 18.

However, both RF and pulsed DC deposited films are not fully dense andmost likely have columnar structures. These columnar structures aredetrimental for optical wave guide applications due to the scatteringloss caused by the structure. By applying a RF bias on wafer 16 duringdeposition, the deposited film can be dandified by energetic ionbombardment and the columnar structure can be substantially eliminated.

In the AKT-1600 based system, for example, target 12 can have an activesize of about 675.70×582.48 by 4 mm in order to deposit films onsubstrate 16 that have dimension about 400×500 mm. The temperature ofsubstrate 16 can be held at between −50 C and 500 C. The distancebetween target 12 and substrate 16 can be between about 3 and about 9cm. Process gas can be inserted into the chamber of apparatus 10 at arate up to about 200 sccm while the pressure in the chamber of apparatus10 can be held at between about 0.7 and 6 millitorr. Magnet 20 providesa magnetic field of strength between about 400 and about 600 Gaussdirected in the plane of target 12 and is moved across target 12 at arate of less than about 20-30 sec/scan. In some embodiments utilizingthe AKT 1600 reactor, magnet 20 can be a race-track shaped magnet withdimension about 150 mm by 600 mm.

A top down view of magnet 20 and wide area target 12 is shown in FIG. 2.A film deposited on a substrate positioned on carrier sheet 17 directlyopposed to region 52 of target 12 has good thickness uniformity. Region52 is the region shown in FIG. 1B that is exposed to a uniform plasmacondition. In some implementations, carrier 17 can be coextensive withregion 52. Region 24 shown in FIG. 2 indicates the area below which bothphysically and chemically uniform deposition can be achieved, wherephysical and chemical uniformity provide refractive index uniformity,for example. FIG. 2 indicates that region 52 of target 12 that providesthickness uniformity is, in general, larger than region 24 of target 12providing thickness and chemical uniformity. In optimized processes,however, regions 52 and 24 may be coextensive.

In some embodiments, magnet 20 extends beyond area 52 in one direction,the Y direction in FIG. 2, so that scanning is necessary in only onedirection, the X direction, to provide a time averaged uniform magneticfield. As shown in FIGS. 1A and 1B, magnet 20 can be scanned over theentire extent of target 12, which is larger than region 52 of uniformsputter erosion. Magnet 20 is moved in a plane parallel to the plane oftarget 12.

The combination of a uniform target 12 with a target area 52 larger thanthe area of substrate 16 can provide films of highly uniform thickness.Further, the material properties of the film deposited can be highlyuniform. The conditions of sputtering at the target surface, such as theuniformity of erosion, the average temperature of the plasma at thetarget surface and the equilibration of the target surface with the gasphase ambient of the process are uniform over a region which is greaterthan or equal to the region to be coated with a uniform film thickness.In addition, the region of uniform film thickness is greater than orequal to the region of the film which is to have highly uniform opticalproperties such as index of refraction, density, transmission orabsorptivity.

Target 12 can be formed of any materials, but is typically metallicmaterials such as, for example, combinations of Al and Si. Therefore, insome embodiments, target 12 includes a metallic target material formedfrom intermetallic compounds of optical elements such as Si, Al, Er andYb. Additionally, target 12 can be formed, for example, from materialssuch as La, Yt, Ag, Au, and Eu. To form optically active films onsubstrate 16, target 12 can include rare-earth ions. In some embodimentsof target 12 with rare earth ions, the rare earth ions can bepre-alloyed with the metallic host components to form intermetallics.See the '341 application.

In several embodiments of the invention, material tiles are formed.These tiles can be mounted on a backing plate to form a target forapparatus 10. FIG. 3A shows an embodiment of target 12 formed withindividual tiles 30 mounted on a cooled backplate 25. In order to form awide area target of an alloy target material, the consolidated materialof individual tiles 30 should first be uniform to the grain size of thepowder from which it is formed. It also should be formed into astructural material capable of forming and finishing to a tile shapehaving a surface roughness on the order of the powder size from which itis consolidated. A wide area sputter cathode target can be formed from aclose packed array of smaller tiles. Target 12, therefore, may includeany number of tiles 30, for example between 2 to 20 individual tiles 30.Tiles 30 are finished to a size so as to provide a margin ofnon-contact, tile to tile, 29 in FIG. 3A, less than about 0.010″ toabout 0.020″ or less than half a millimeter so as to eliminate plasmaprocesses between adjacent ones of tiles 30. The distance between tiles30 of target 12 and the dark space anode or ground shield 19, in FIG. 1Bcan be somewhat larger so as to provide non contact assembly or providefor thermal expansion tolerance during process chamber conditioning oroperation.

Several useful examples of target 12 that can be utilized in apparatus10 according to the present invention include the following targetscompositions: (Si/Al/Er/Yb) being about (57.0/41.4/0.8/0.8),(48.9/49/1.6/0.5), (92/8/0/0), (60/40/0/0), (50/50/0/0), (65/35/0/0),(70/30/0,0), and (50,48.5/1.5/0) cat. %, to list only a few. Thesetargets can be referred to as the 0.8/0.8 target, the 1.6/0.5 target,the 92-8 target, the 60-40 target, the 50-50 target, the 65-35 target,the 70-30 target, and the 1.5/0 target, respectively. The 0.8/0.8,1.6/0.5, and 1.5/0 targets can be made by pre-alloyed targets formedfrom an atomization and hot-isostatic pressing (HIPing) process asdescribed in the '341 application. The remaining targets can be formed,for example, by HIPing. Targets formed from Si, Al, Er and Yb can haveany composition. In some embodiments, the rare earth content can be upto 10 cat. % of the total ion content in the target. Rare earth ions areadded to form active layers for amplification. Targets utilized inapparatus 10 can have any composition and can include ions other thanSi, Al, Er and Yb, including: Zn, Ga, Ge, P, As, Sn, Sb, Pb, Ag, Au, andrare earths: Ge, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy Ho, Er, Tm Yb and Lu.

Optically useful materials to be deposited onto substrate 16 includeoxides, fluorides, sulfides, nitrides, phosphates, sulfates, andcarbonates, as well as other wide band gap semiconductor materials. Toachieve uniform deposition, target 12, itself can be chemically uniformand of uniform thickness over an extended area.

Target 12 can be a composite target fabricated from individual tiles,precisely bonded together on a backing plate with minimal separation, asis discussed further with respect to FIG. 3. In some embodiments, themixed intermetalllics can be plasma sprayed directly onto a backingplate to form target 12. The complete target assembly can also includesstructures for cooling the target, embodiments of which have beendescribed in U.S. Pat. No. 5,565,071 to Demaray et al, and incorporatedherein by reference.

Substrate 16 can be a solid, smooth surface. Typically, substrate 16 canbe a silicon wafer or a silicon wafer coated with a layer of siliconoxide formed by a chemical vapor deposition process or by a thermaloxidation process. Alternatively, substrate 16 can be a glass, such asCorning 1737 (Corning Inc., Elmira, N.Y.), a glass-like material,quartz, a metal, a metal oxide, or a plastic material. Substrate 16 canbe supported on a holder or carrier sheet that may be larger thansubstrate 16. Substrate 16 can be electrically biased by power supply18.

In some embodiments, the area of wide area target 12 can be greater thanthe area on the carrier sheet on which physically and chemically uniformdeposition is accomplished. Secondly, in some embodiments a centralregion on target 12, overlying substrate 16, can be provided with a veryuniform condition of sputter erosion of the target material. Uniformtarget erosion is a consequence of a uniform plasma condition. In thefollowing discussion, all mention of uniform condition of target erosionis taken to be equivalent to uniform plasma condition. Uniform targeterosion is evidenced by the persistence of film uniformity throughout anextended target life. A uniformly deposited film can be defined as afilm having a nonuniformity in thickness, when measured atrepresentative points on the entire surface of a substrate wafer, ofless than about 5% or 10%. Thickness nonuniformity is defined, byconvention, as the difference between the minimum and maximum thicknessdivided by twice the average thickness. If films deposited from a targetfrom which more than about 20% of the weight of the target has beenremoved continue to exhibit thickness uniformity, then the sputteringprocess is judged to be in a condition of uniform target erosion for allfilms deposited during the target life.

As shown in FIG. 1B, a uniform plasma condition can be created in theregion between target 12 and substrate 16 in a region overlyingsubstrate 16. A plasma 53 can be created in region 51, which extendsunder the entire target 12. A central region 52 of target 12, canexperience a condition of uniform sputter erosion. As discussed furtherbelow, a layer deposited on a substrate placed anywhere below centralregion 52 can then be uniform in thickness and other properties (i.e.,dielectric, optical index, or material concentrations).

In addition, region 52 in which deposition provides uniformity ofdeposited film can be larger than the area in which the depositionprovides a film with uniform physical or optical properties such aschemical composition or index of refraction. In some embodiments, target12 is substantially planar in order to provide uniformity in the filmdeposited on substrate 16. In practice, planarity of target 12 can meanthat all portions of the target surface in region 52 are within a fewmillimeters of a planar surface, and can be typically within 0.5 mm of aplanar surface.

Other approaches to providing a uniform condition of sputter erosionrely on creating a large uniform magnetic field or a scanning magneticfield that produces a time-averaged, uniform magnetic field. Forexample, rotating magnets or electromagnets can be utilized to providewide areas of substantially uniform target erosion. For magneticallyenhanced sputter deposition, a scanning magnet magnetron source can beused to provide a uniform, wide area condition of target erosion.

As illustrated in FIG. 1A, apparatus 10 can include a scanning magnetmagnetron source 20 positioned above target 12. An embodiment of ascanning magnetron source used for dc sputtering of metallic films isdescribed in U.S. Pat. No. 5,855,744 to Halsey, et. al., (hereafter'744), which is incorporated herein by reference in its entirety. The'744 patent demonstrates the improvement in thickness uniformity that isachieved by reducing local target erosion due to magnetic effects in thesputtering of a wide area rectangular target. As described in the '744patent, by reducing the magnetic field intensity at these positions, thelocal target erosion was decreased and the resulting film thicknessnonuniformity was improved from 8%, to 4%, over a rectangular substrateof 400×500 mm.

The process gas utilized in reactor 10 includes an inert gas, typicallyargon, used as the background sputtering gas. Additionally, with someembodiments of target 12, reactive components such as, for example,oxygen may be added to the sputtering gas. Other gasses such as N₂, NH₃,CO, NO, CO₂, halide containing gasses other gas-phase reactants can alsobe utilized. The deposition chamber can be operated at low pressure,often between about 0.5 millitorr and 8-10 millitorr. Typical processpressure is below about 3-5 millitorr where there are very fewcollisions in the gas phase, resulting in a condition of uniform “freemolecular” flow. This ensures that the gas phase concentration of agaseous component is uniform throughout the process chamber. Forexample, background gas flow rates in the range of up to about 200 sccm,used with a pump operated at a fixed pumping speed of about 50liters/second, result in free molecular flow conditions.

The distance d, in FIG. 1A, between target 12 and substrate 16 can, insome embodiments, be varied between about 4 cm and about 9 cm. A typicaltarget to substrate distance d is about 6 cm. The target to substratedistance can be chosen to optimize the thickness uniformity of the film.At large source to substrate distances the film thickness distributionis dome shaped with the thickest region of the film at the center of thesubstrate. At close source to substrate distance the film thickness isdish shaped with the thickest film formed at the edge of the substrate.The substrate temperature can be held constant in the range of about−40° C. to about 550° C. and can be maintained at a chosen temperatureto within about 10° C. by means of preheating substrate 16 and thesubstrate holder prior to deposition. During the course of deposition,the heat energy impressed upon the substrate by the process can beconducted away from substrate 16 by cooling the table on which substrate16 is positioned during the process, as known to those skilled in theart. The process is performed under conditions of uniform gasintroduction, uniform pumping speed, and uniform application of power tothe periphery of the target as known to skilled practitioners.

The speed at which a scanning magnet 20 can be swept over the entiretarget can be determined such that a layer thickness less than about 5to 10 Å, corresponding roughly to two to four monolayers of material, isdeposited on each scan. Magnet 20 can be moved at rates up to about 30sec/one-way scan and typically is moved at a rate of about 4 sec/one-wayscan. The rate at which material is deposited depends on the appliedpower and on the distance d, in FIG. 1A, between the target 12 and thesubstrate 16. For deposition of optical oxide materials, for examplescanning speeds between about 2 sec/one-way scan across the target to20-30 sec/scan provide a beneficial layer thickness. Limiting the amountof material deposited in each pass promotes chemical and physicaluniformity of the deposited layer.

Substrate bias has been used previously to planarize RF sputtereddeposited quartz films. A theoretical model of the mechanism by whichsubstrate bias operates, has been put forward by Ting et al. (J. Vac.Sci. Technol. 15, 1105 (1978)). When power is applied to the substrate,a so-called plasma sheath is formed about the substrate and ions arecoupled from the plasma. The sheath serves to accelerate ions from theplasma so that they bombard the film as it is deposited, sputtering thefilm, and forward scattering surface atoms, densifying the film andeliminating columnar structure. The effects of adding substrate bias areakin to, but more dramatic than, the effects of adding the low frequencyRF component to the sputter source.

Biasing substrate 16 results in the deposited film being simultaneouslydeposited and etched. The net accumulation of film at any point on asurface depends on the relative rates of deposition and etching, whichdepend respectively, on the power applied to the target and to thesubstrate, and to the angle that the surface makes with the horizontal.The rate of etching is greatest for intermediate angles, on the order of45 degrees, that is between about 30 and 60 degrees.

Powers to target 12 and substrate 16 can be adjusted such that the ratesof deposition and etching are approximately the same for a range ofintermediate angles. In this case, films deposited with bias sputteringhave the following characteristics. At a step where a horizontal surfacemeets a vertical surface, the deposited film makes an intermediate anglewith the horizontal. On a surface at an intermediate angle, there willbe no net deposition since the deposition rate and etch rate areapproximately equal. There is net deposition on a vertical surface.

Target 12 can have an active size of about 675.70×582.48 by 4 mm, forexample, in a AKT-1600 based system in order to deposit films on asubstrate 16 that is about 400×500 mm. The temperature of substrate 16can be held at between −50 C and 500 C. The distance between target 12and substrate 16 can be between 3 and 9 cm. Process gas can be insertedinto the chamber of apparatus 10 at a rate of between about 30 to about100 sccm while the pressure in the chamber of apparatus 10 can be heldat below about 2 millitorr. Magnet 20 provides a magnetic field ofstrength between about 400 and about 600 Gauss directed in the plane oftarget 12 and is moved across target 12 at a rate of less than about20-30 sec/scan.

Therefore, any given process utilizing apparatus 10 can be characterizedby providing the power supplied to target 12, the power supplied tosubstrate 16, the temperature of substrate 16, the characteristics andconstituents of the reactive gasses, the speed of the magnet, and thespacing between substrate 16 and target 12.

Sputtered oxide films according to some embodiments of the presentinvention can be deposited onto a Si wafer or thermal oxide wafers atpressure of between about 3 and about 6 mTorr. The ratio of O₂/Ar gasflow can be set at a value to ensure that target 12 is operating withina poison mode. The poison mode is defined as the ratio where the oxideis etched from the surface of target 12 as fast as the oxide layer isformed. Operating in the poison mode results in the stoichiometric film.Sub-stoichiometric oxides may not be optically transparent. The pulsingfrequency range for power supply 14 can be from about up to about 250KHz. The frequency 40 KHz is approximately the lowest frequency at whichno arcing will occur during deposition in, for example, the AKT 1600based system. The reverse pulsing time is determined by the amount ofarcing generated during the process. Longer reverse time means longerdischarge time and thus less arcs. However, if the reverse time is toolong, the deposition rate will decrease. Power supply 18 is a 2 MHz RFpower supply operated at powers up to several hundred Watts.

FIG. 4 shows an embodiment of a process procedure 400 performed onapparatus 10. In step 401, the target is prepared for the deposition. Insome embodiments, target 12 can be cleaned by pure Ar sputtering. Inother words, apparatus 10 is operated with pure Ar gas only (referred toas the metal mode) in order to sputter away a surface layer of target12.

FIG. 7 shows the typical drift in the index of refraction withdeposition of oxide layers for several different targets over differentruns for each target. In FIG. 7, the compositions of the targetmaterials utilized in target 12 for the depositions shown are asfollows: Si: 60 cat. % and Al: 40 cat. %; Si: 50 cat. % and Al: 50 cat.%; Si: 85 cat. % and Al: 15 cat. %; Si: 35 cat. % and Al: 65 cat. %; andSi: 92 cat. % and 8 cat. %. Each deposition was operated under the sameprocess parameters: 4.5 kW of pulsed DC power at 200 kHz with a reversetime of 2.3 μs applied to target 12, O₂ flow at 44 sccm, Ar flow at 30sccm introduced to apparatus 10, 100 W of bias power at 2 MHz applied tosubstrate 16, the temperature of substrate 16 held at 200° C., and thedistance between substrate 16 and target 12 being set at 6 cm. For eachtarget measured, the index drifted up during repeated utilization.

FIG. 8 shows the relationship between the index of refraction of a filmdeposited according to the present invention and the amount of aluminumin the composite target. As can be seen from FIG. 8, the index ofrefraction of the deposited film depends strongly on the aluminumcontent. Therefore, as the aluminum in a metal target is depleted, theindex of refraction drifts. In some embodiments, the ratio of Ar and O₂utilized in the process can be maintained to provide films of uniformindex over a large number of depositions on the target.

Reactive sputtering from a metal or metallic alloy target 12 can becharacterized by two modes of operation. In the first mode, which issometimes referred to as the ‘metallic mode’ the surface of target 12 issubstantially metallic. This mode is characterized by a small additionof reactive gas to the inert gas flow of apparatus 10 as well as ahigher impedance magnetron discharge. It is also characterized byincomplete oxidation of film deposited on substrate 16 and thereforehigher index films. As the proportion of reactive to inert gas isincreased, the sputter voltage at target 12 begins to fall at constantpower.

FIG. 5 shows the voltage on target 12 of an embodiment of apparatus 10according to the present invention as a function of process gasconstitution. In the example illustrated in FIG. 5, for example, ametallic target with composition 0.8 cat. % Er, 0.8 cat. % Yb, 57.4 cat.% Si and 41 cat. % Si, which can be formed as described in the '341application, was sputtered in an embodiment of apparatus 10 based on theAKT-1600 PVD system with 6 kW of pulsed DC power at a frequency of 120kHz and a reverse time of 2.3 micro seconds. The Argon gas flow was setat 60 sccm and the Oxygen gas flow was varied from zero up to 40 sccm.For more details regarding this deposition, see Example 1 below.

As shown in FIG. 5, the voltage on target 12 during deposition (the“target voltage”) was constant at about 420 Volts for oxygen flow ratesup to about 20 sccm. This is clearly the metallic mode of operation forthis embodiment of target 12. Films deposited in this range of oxygenflow are characterized as metallic with an oxygen content that increaseswith oxygen flow rate during deposition. As the oxygen flow is increasedup to about 26 sccm, the voltage on target 12 begins to decrease,indicating that the surface of target 12 is beginning to form an oxidelayer. The oxide layer on the surface of target 12 has a highersecondary electron yield under the influence of the Argon ion flux. Theadditional electron flux to the magnetron electron trap increases theion production in the plasma, which, in turn, decreases the impedance ofthe plasma discharge in apparatus 10.

At slightly higher oxygen flow during deposition, the oxide layer ontarget 12 forms a continuous layer and the voltage of target 12 duringdeposition falls rapidly to the range of about 190 to about 270 Volts,indicating complete coverage of the surface of target 12 with an oxidethat is at least as thick as the material removed during one scan of themagnetron. Under this condition, the rate of oxide formation on thesurface of target 12 equals or exceeds the rate of sputter removal ofthe surface of target 12 by the moving magnetron 20. This condition issometimes referred to as the ‘poisoned mode’.

Under steady state DC voltage conditions, the oxide layer on target 12soon charges up, leading to reduced rate of sputtering and increasedmicro-arc discharging in apparatus 10. This discharging leads toparticulation of the oxide layer on target 12, which degrades thequality of a film deposited on substrate 16. In the example shown withFIG. 5, the negative going DC Voltage is reduced at a frequency of 120kHz to a positive value for a period of about 2.3 micro seconds percycle, allowing charge neutralization of the surface of target 12,increasing the steady state sputter and deposition rates as well asdecreasing the rate of micro-arcing.

In the case of a magnetron configuration of magnet 20 having asignificant deep local target erosion (rather than a configuration ofmagnet 20 described above which yields uniform target erosion), thechange in the target voltage of target 12 is more gradual withincreasing oxygen flow since it is more difficult to establish an oxidecondition at the center of an intense region of local erosion. Theresulting deposited film, however, will be rich in metallic sputteredflux to the substrate in the region of higher sputter erosion, leadingto non uniform stoicheometry and non-uniform indices of refraction in afilm deposited on substrate 16. In the case of a scanning magnetron 20with uniform target erosion, the change in the surface condition frommetallic to poisoned is more abrupt, as the formation rate of the oxideincreases to equal the sputter removal of the oxide over a wide area ofthe target. In this case, there is uniform distribution of sputteredoxide from the target. Uniform stoicheometry and uniform indices ofrefraction result for the film deposited on substrate 16.

FIG. 8 shows the range of indices of refraction of films deposited fortargets of differing silica and alumina compositions, as deposited andafter a subsequent anneal step. In the case of a pure silicon target,the as-deposited index of refraction can be as high as 3.4 for pureamorphous silicon. In FIG. 8, pure silica films (zero Al %) can bedeposited with a reactive pulsed DC and substrate bias depositionaccording to the present invention with substantially complete oxygenstoicheometry, so as to approximate monolithic amorphous silica. Theindex of refraction of such films decreases with a subsequent heattreatment of between about 700-900° C., indicating somewhat morecomplete oxidation reaction of the material of the film together withsome degree of stress relaxation of the film deposited on substrate 16.

At the opposite extreme, a pure aluminum embodiment of target 12 (100%Al) can be utilized to deposit films on substrate 16 under similarprocess conditions as is utilized to deposit pure silica films onsubstrate 16. In the case of the pure aluminum reactive deposition, thedependence of the index of refraction of the film deposited on substrate16 on oxygen flow as well as on the frequency of the pulsed DC processcan be examined. As a result, a larger range of effective index ofrefraction is achieved together with a reduced or zero dependence of theindex on the subsequent anneal process. Six targets having differingaluminum composition were utilized to evaluate the index of refractionof sputtered films on substrate 16 of related composition. The largestchange of index with the sputtering conditions is achieved forcomposition near the middle of the Al/Si composition range (about 50% Aland 50% Si).

FIG. 7 shows the change in film index for oxide films for severalembodiments of target 12 and processes with an initial 30 minutes ofArgon only sputtering, followed by continuous deposition with an oxygenflow rate sufficient for operation in the poisonous mode. Note that therate of increase in the index of refraction of a resulting filmdeposited on substrate 16 with continuous poisoned mode deposition isproportional to the concentration of aluminum in the composition oftarget 12. This result is due to the depletion of the aluminum from thetarget surface during the metallic sputtering or pre-condition process.The aluminum in target 12 is preferentially sputtered over the siliconin target 12, leaving the surface of target 12 rich in silicon. At theonset of poisoned mode sputtering, the film deposited on substrate 16 isrich in silica and demonstrates a systematic and reproducible decreasein index of refraction. During continuous poisoned mode deposition, thesilicon rich surface of target 12 can be sputtered away and the aluminumportion substantially returned to the bulk composition of target 12.Consequently, a metallic precondition step can be utilized to achieve asubsequent process for the deposition of a film having an increasingindex of refraction under conditions of oxide/metal stoicheometry.

In step 402 of FIG. 4, substrate 16 is prepared. Substrate 16 can bemounted on carrier sheet 17 and placed in apparatus 10. In step 403, gasflow parameters are adjusted for the particular deposition to beperformed. The constituency and flow rates of the process gas are fixed.In some embodiments, the ratio of Ar and O₂, for example, can be set andthe flow rate of each gas set. Further, the combination of flow rate andvacuum system of apparatus 10 determines the pressure during depositionin apparatus 10.

In step 404, the substrate temperature is set. Substrate 16 may bebrought to temperature over a period of time. In step 405, the scancharacteristics of magnet 20 are fixed. In step 406, the power settingfor power supply 18 is set. Finally, in step 407, the parameters ofpulsed DC power supply 14 is set, including the power, frequency, andreverse pulsing time. In step 408, then, a film that depends oh theparameters of reactor apparatus 10 is deposited on substrate 16. In someembodiments, films deposited by procedure 400 are thermally annealedafter deposition.

FIG. 4 illustrates an example deposition process only. Embodiments ofdeposition, processes according to the present invention can beperformed in various different orders.

FIG. 9 shows a chart of various deposition parameters according to thepresent invention for various embodiments of target 12 and the indicesof refraction, both before and after an anneal step, for the resultingdeposited film on substrate 16. Each deposition was accomplished with anembodiment of apparatus 10 based on the AKT 1600 PVD reactor. Annealswere accomplished at 725° C. for 30 min. Specific examples of particulardepositions and characteristics of the resulting films deposited onsubstrate 16 are further discussed below.

FIG. 10 shows the dependence of the index of refraction of silica layersdeposited according to the present invention with process conditions.FIG. 11 shows the dependence of index of refraction on the O2/Ar flowratio for the deposition of pure alumina according to the presentinvention. FIG. 12 shows the dependence of index for pure alumina filmson the frequency of the pulsed DC power applied to target 12. Bothparameters can be utilized to reliably control the index of refractionof films deposited on substrate 16 over a range of index values withoutthe use of an additional cationic species, a so called ‘dopant’. A thirdprocess parameter that can be utilized to adjust the index of refractionof a film deposited on substrate 16 is the bias power applied tosubstrate 16. Increasing the oxygen flow ratio, the frequency of thepulsed DC power applied to target 12 or the bias power applied tosubstrate 16 will systematically increase the index of refraction of thealumina film deposited on substrate 16. In the case of pure aluminafilms, minor to no change in the index occurs due to a subsequent annealprocess.

FIG. 13 shows the index of refraction of a film deposited on substrate16 from an embodiment of target 12 with about 92 cat. % of Si and about8 cat. % of Al for a series of sequential depositions in an embodimentof apparatus 10 based on the AKT 4300 PVD reactor, each following ametallic process condition. For constant high oxygen flow conditions, asmall upward trend in the index of refraction is observed. As isgenerally true, the index of films deposited with higher substrate biaspower is systematically lower than films deposited without substratebias.

FIG. 14 shows the upward trend of the index of refraction after metallicmode precondition of an embodiment of target 12 having composition ofabout 83 cat. % Si and about 17 cat. % Al for a series of depositions inan embodiment of apparatus 10 based on the AKT 1600 PVD reaction. As isshown in FIG. 14, longer metallic preconditioning of target 12 resultsin the index of refraction of the films deposited on substrate 16 havinga higher rate of increase than for cases with less prolonged metallicpreconditioning of target 12. The vertical lines on FIG. 14 indicateplaces where target 12 was preconditioned with only Ar for the indicatedperiods of time. FIG. 15 shows a decrease in the change in index forsequential films with this embodiment of target 12 deposited withreduced oxygen flow rates at a constant total pressure. A flow rate foroxygen was determined so that the run to run variation for the index ofrefraction of the film deposited on substrate 16 from this target wasabout 0.0001, (see the circled data points on the graph of FIG. 15)which is similar to the variance of the index over the entire wafer ofsubstrate 16, which is about 70 parts per million.

In some embodiments, films deposited by a pulsed DC biased methodaccording to the present invention are uniformly amorphous throughouttheir thickness. As has been discussed above, biasing of substrate 16leads to densification and uniformity in the deposited film. FIGS. 16Athrough 16D show a TEM photograph of a film 1601 deposited according tothe present invention. Further, diffraction patterns shown in FIGS. 16B,16C and 16D at points a, b and c, respectively, in deposited film 1601show that the film is ammorphous through the thickness of the film. Thediffraction patterns of FIGS. 16B, 16C and 16D show no effects ofcrystallization. Further, the smoothness of the surface of film 1601indicates a defect free film. The film deposited in FIG. 16A isdeposited with an 0.8/0.8 target (i.e., a target having the composition52.0 cat. % of Si, 41.0 cat. % of Al, 0.8 cat. % of Er and 0.8 cat. % ofYb). The film is deposited at 6 kW of 120 kHz pulsed DC power with areverse time of 2.3 μs. The Argon and Oxygen flow rates are 60 sccm and28 sccm, respectively. Substrate 16 is biased with 100 W of power.

FIG. 17 shows the optical loss per centimeter, measured at 1310 nm,using a three prism coupling to the so called slab mode of the film on a10 micron oxide, silicon wafer. As deposited the biased, pulsed DC filmfrom a 60 cat. % Si and 40 cat. % Al film demonstrated about 0.1 dB/cmloss. After an 800° C. anneal in air, the loss was less than themeasurement sensitivity of the prism coupling method. This data clearlydemonstrates that films deposited according to embodiments of thepresent invention can be used for the purpose of constructing low lossplanar light wave circuits.

Deposition of films according to the present invention can be utilizedto deposit cladding layers, active core layers, and passive core layersof an optical amplifier structure or optical waveguide structure. Insome applications, for example multiplexer structures, the separationbetween adjacent waveguides can be small, for example about 8 μm. Insome embodiments, the deposition parameters of the upper cladding layercan be adjusted to not only adjust the index of refraction of the layer,but also to insure that the spacing between adjacent waveguides issmall.

FIG. 18 shows an example planarization deposition over a multiplexerstructure. In the particular example of upper cladding layer 1803 shownin FIG. 18, the deposition parameters from a 92 cat. % Si and 8 cat. %Al is: 5.5 Kw of Pulsed DC power applied at 200 KHz with 2.2 μs ofreverse time, gas flow of 75 sccm Ar and 100 sccm O₂, a substrate biasof 650 W (at 2 MHz), and a substrate temperature of 200° C. Layer 1803was deposited with an AKT 4300 based embodiment of apparatus 10. Asshown in FIG. 18, the layer thickness in areas other than over waveguidestructures 1801 and 1802 is 11.4 μm. Waveguide structures 1801 and 1802are 8.20 μm high waveguides and separated by 6.09 μm at the base and by8.40 μm at their top. In FIG. 18, the undercladding layer 1804 is about1.98 μm thick.

FIG. 19 illustrates deposition of material over a structure. Uppercladding layer 1803, in region 1901, will be angled from the horizontalby an angle θ. The deposition and etching rates of a deposited layerdepends on the angle θ. FIGS. 20 and 21 illustrate different cases ofdeposition and etch rates as a function of the angle θ. The relationshipbetween the rate of deposition and the etch rates can be adjusted byadjusting the deposition parameters. For example, the bias power tosubstrate 16 can be adjusted to control the relationship between theetch rates and deposition rates of material.

FIG. 22 illustrates deposition rates over a structure 2201 as a functionof time. In FIG. 2201, h is the thickness deposited over structure 2201.The planarization when layer 1803 becomes flat.

The time for planarization can be estimated as

${t_{p} = \frac{{\frac{W}{2}\tan\;\alpha} + H}{a_{flat} - \frac{a_{\min}}{\cos\;\alpha}}},$where W is the width of structure 2201, H is the height of structure2201, a_(flat) refers to the accumulation rate on the flat surface,a_(min) refers to the accumulation rate on the minimum accumulationslope, and α is the surface angle from the horizontal plane of theminimum accumulation slope.

FIG. 23 shows a deposited film 1803 as shown in FIG. 18, except that thebias power to substrate 16 is set to 400 W instead of 650 W. As can beseen in FIG. 23, a keyhole 2301 is formed with an incomplete filling ofuppercladding layer 1803 between structures 1801 and 1802. Deposition ofuppercladding layer 1803 substantially follows the trends illustrated inFIGS. 19 through 22.

FIG. 24 shows deposition as shown in FIG. 18, except that the bias powerto substrate 16 is set to 600 W instead of 650 W; As can be seen in FIG.24, keyhole 2301 has closed leaving a small line defect 2401 in thefill.

FIG. 28 shows deposition as shown in FIG. 18, except that the bias powerto substrate 16 is set to 900 W instead of 650 W. As can be seen in FIG.28, the etch rate has been increased to such an extent that the cornersof structures 1801 and 1802 have been etched to form slopes 2501 and2502, respectively.

Therefore, as illustrated in FIGS. 18 through 25, an uppercladding layercan be deposited in accordance with the present invention such that itfills the space between adjacently placed waveguides. In general, theparameters can be optimized for index control and the bias power tosubstrate 16 can be adjusted for fill. In some embodiments, otherparameters (e.g., the constituency of process gas, frequency and powerof pulsed DC power source 14, and other parameters) in order to adjustthe deposition and etch rates and thereby effectively planarize thestructure as described.

Therefore, depositions of various films in embodiments of apparatus 10according to the present invention with several embodiments of target 12and the effects on index of refraction, uniformity of films, and fillcharacteristics of varying several of the process parameters has beendiscussed above. In some embodiments, stress effects due to wafer bowingof substrate 16 can also be reduced. Wafer bowing of substrate 16 can bereduced, reducing the stress in a film deposited on substrate 16, by,for example, depositing a film on the backside of substrate 16 beforedeposition of a film on substrate 16. In some embodiments, a film havinga similar thickness of a similar layer of material can be deposited onbackside of substrate 16 prior to deposition of the film on substrate 16according to the present invention. The wafer bowing resulting fromdiffering thermal expansions of the film and substrate 16 is thereforecountered by a similar stress from another film deposited on thebackside of substrate 16.

Several specific examples film depositions utilizing apparatus 10 arediscussed below. Further, examples of optical amplifiers producedutilizing the ceramic tiles according to the present invention arepresented. These examples are provided for illustrative purposes onlyand are not intended to be limiting. Unless otherwise specified,apparatus 10 utilized in the following examples was based on the AKT1600 reactor. Further, unless otherwise specified, the temperature ofsubstrate 16 was held at about 200° C. and the distance betweensubstrate 16 and target 12 was 4 s/scan. The separation betweensubstrate 16 and target 12 is about 6 cm.

EXAMPLE 1

An AKT 1600 based reactor can be utilized to deposit a film. In thisexample, a wide area metallic target of dimension 550×650 mm withcomposition (Si/Al/Er/Yb) being about 57.0 cat. % Si, 41.4 cat. % Al,0.8 cat. % Er, and 0.8 cat. % Yb (a “0.8/0.8” target) was fabricated asdescribed in the '341 application.

In step 402, a 150 mm P-type silicon wafer substrate was placed in thecenter of a 400×500 mm glass carrier sheet 17. Power supply 14 was setto supply 6000 watts of pulse DC power at a frequency of 120 KHz with areverse pulsing time of about 2.3 us. Magnet 20, which is a race-trackshaped magnet of approximate dimension 150 mm×600 mm, was swept over thebackside of the target at a rate of about 4 seconds per one-way scan.The temperature of substrate 16 was held at 200 C and 100 W of 2 MHz RFpower was applied to substrate 16. The target 12 to substrate 16distance was about 6.5 cm. The sputtering gas was a mixture of Argon andOxygen. Substrate 16 and carrier 17 was preheated to 350° C. for atleast 30 min prior to deposition. The active film was deposited in thepoison mode. Deposition efficiency was approximately 1 um/hr.

FIG. 5 shows the hysteresis curve of this particular embodiment oftarget 12. When target 12 under goes the transition from metallic topoison mode, the target voltage drops from an average of about 420V toan average of about 260V. Before each film deposition, in step 401,target 12 is cleaned by pure Argon sputtering in the metallic mode. Thentarget is then conditioned in poison mode with the oxygen flow muchhigher than the flow required at the transition region.

Tables 1A through 1C shows some effects on the deposited films ofdepositions with the 0.8/0.8 target under different operatingconditions. Table 1A includes photoluminescence (pumped at 532 nm) andindex of refraction for films deposited on substrate 16 with differentAr/O₂ gas flow ratios with no bias power applied to substrate 16.

TABLE 1A Target Reverse Power Frequency Pulsing Bias PL/um (KW) Ar/O2(KHz) Time (us) (W) (532 nm) Index 6 30/42 200 2.3 0 1973 1.5142 6 30/36200 2.3 0 2358 1.5215 6 60/30 200 2.3 0 3157 1.5229 6 60/28 200 2.3 03421 1.5229

Table 1B shows the variation in photoluminescence (pumped at 532 nm) andindex of refraction of the film deposited on substrate 16 withdeposition processes having with the same Ar/O₂ ratios but differentpulsed DC power frequencies from power supply 14.

TABLE 1B Target Reverse Power Frequency Pulsing Bias PL/um (KW) Ar/O2(KHz) Time (us) (W) (532 nm) Index 3 60/28 100 2.3 100 1472 1.5146 460/28 75 3.5 100 2340 1.5189 6 60/28 120 2.3 100 5178 1.5220

Table 1C shows the photoluminescence and index as deposited where thebias power to substrate 16 is varied.

TABLE 1C Target Reverse Power Frequency Pulsing Bias PL/um (KW) Ar/O2(KHz) Time (us) (W) (532 nm) Index 6 60/28 200 2.3 0 3657 1.5230 6 60/28200 2.3 100 2187 1.5244 6 60/28 200 2.3 200 3952 1.5229 6 60/28 200 2.3300 5000 1.5280

The photoluminescence values can be measured with a Phillips PL-100. Thedeposited film can be pumped with a 532 nm laser and the luminescence at980 is measured. The index is the index of refraction. Typically, filmsdeposited are annealed in order to activate the erbium. FIG. 6 shows thephotoluminescence and lifetime versus anneal temperature for a typicalfilm deposited as described in this example.

EXAMPLE 2

A waveguide amplifier can be deposited according to the presentinvention. An embodiment of target 12 having composition 57.4 cat. % Si,41.0 cat. % Al, 0.8 cat. % Er 0.8 cat. % Yb (the “0.8/0.8 target”) canbe formed as disclosed in the '341 application. The Er—Yb (0.8/0.8)co-doped Alumino-Silicate film was deposited onto a 6 inch wafer ofsubstrate 16 which includes a 10 μm thick thermal oxide substrate, whichcan be purchased from companies such as Silicon Quest International,Santa Clara, Calif. Target 12 was first cleaned by sputtering with Ar(80 sccm) only in the metallic mode. Target 12 was then conditioned inpoison mode by flowing 60 sccm of Argon and 40 sccm of oxygenrespectively. The power supplied to target 12 during conditioning waskept at about 6 kW.

An active core film was then deposited on substrate 16. The thickness ofthe deposited film is approximately 1.2 μm. The deposition parametersare shown in Table 2.

TABLE 2 Target Pulsing Reverse Power Ar/O2 Frequency Bias pulsing (KW)(sccm) (KHz) (W) time (us) 6 60/28 120 100 2.3

A straight waveguide pattern can then formed by standardphotolithography techniques. The active core was etched using reactiveion etch followed by striping and cleaning. Next, a 10 μm top claddinglayer is deposited using a similar deposition process according to thepresent invention. An embodiment of target 12 with composition 92 cat. %Si and 8 cat. % Al as shown in FIG. 9 to form the top cladding layer.The index difference between the top cladding layer and the active layeris about 3.7%. The amplifier is then annealed at 725° C. for about 30min (see FIG. 6, for example).

The erbium excited-state lifetime and the up-conversion coefficient weremeasured to be 3 ms and 4.5×10⁻¹⁸ cm³/s, respectively. A net gain ofabout 4 dB for small signal (about −20 dBm) with fiber to waveguide andto fiber coupling was obtained. Waveguide length was 10 cm and the widthwas about 1.5 to 8 μm. The coupling loss between the fiber and thewaveguide is 3-4 dB/facet, and passive excess loss is 0.1-0.2 dB/cm for3 um waveguide. The waveguide was both co- and counter pumped with 150mW 980 nm laser per facet.

EXAMPLE 3

This example describes production of a dual core Erbium/Yttrbiumco-doped amplifier according to the present invention. In one example,substrate 16 is a silicon substrate with an undercladding layer ofthermally oxidized SiO₂ of about 15 μm thick. Substrate 16 with thethermal oxide layer can be purchased from companies such as SiliconQuest International, Santa Clara, Calif. A layer of active core materialis then deposited on substrate 16 with a Shadow Mask as described in the'492 application. Use of a shadow mask results in a vertical taper oneach side of a finished waveguide which greatly enhances the coupling oflight into and out of the waveguide.

Active core layer is deposited from a 0.8/0.8 target as described in the'247 application having composition 57.4 cat. % Si, 41.0 cat. % Al, 0.8cat. % Er, and 0.8 cat. % Yb. The deposition parameters are identical tothat of Example 2 described above. The active layer is deposited to athickness of about 1.2 μm.

A passive layer of aluminasilicate is then deposited over the activelayer. A passive layer of about 4.25 μm thickness can be deposited withan embodiment of target 12 having composition of Si/Al of about 87 cat.% Si and about 13 cat. % Al. The passive layer and active layer are thenpatterned by standard lithography techniques to form a core that has awidth of about 5.0 μm for the active core and tapering to about 3.5 μmat the top of the passive core with an effective length of about 9.3 cm.

Upper cladding layer is then deposited from a Si/Al target of 92 cat. %Si and 8 cat. % Al. Deposition of the upper cladding layer is shown inFIG. 9. In some embodiments, the upper cladding layer can be depositedwith a non-biased process. The thickness of the upper cladding layer canbe about 10 μm. The amplifier formed by this process is then annealed at725° C. for about 30 min.

The as-deposited Erbium and Ytterbium concentrations in the active layerof core 303 is 2.3×10²⁰ cm⁻³ Erbium concentration and 2.3×10²⁰ cm⁻³Ytterbium concentration. The index of the core is 1.508 and the index ofcladding layers are 1.4458 for undercladding layer 302 and 1.452 foruppercladding layer 304. The parameter Δn/n is therefore about 5.0%.

A reverse taper mode size converter, see the '492 application, isutilized for coupling light into waveguide amplifier 300. The insertionloss at 1310 nm is about 2 dB. FIG. 26 shows the amplifier performanceof this example. In FIG. 26, amplifier 300 is pumped with 150 mW fromone side pumping with 984 nm light. Gain flattening is achieved withinabout 1 dB in the range 1528 nm to 1562 nm for small input signals (−20dBm). For large input signals (0 dBm), gain flattening is also achievedwithin about 1 dB.

EXAMPLE 4

Another example of production of a waveguide amplifier is describedhere. Again, substrate 16 can be a Si wafer with about a 15 μm thickthermal oxide as can be purchased from Silicon Quest International,Santa Clara, Calif. The embodiment of target 12 for the deposition ofthe active core can have a composition of about 50 cat. % Si, 48.5 cat.% Al, 1.5 cat. % Er (the “1.5/0” target), which can be fabricated asdiscussed in the '138 application. Target 12 was first cleaned bysputtering with Ar (80 sccm) only in the metallic mode. Target 12 wasthen conditioned in poison mode by flowing 60 sccm of Argon and 40 sccmof oxygen respectively.

The pulsed DC power supplied to target 12 was about 6 kW. Whenever abrand new target was used or when the target has been expose toatmosphere, a long time of condition (for example more than 30 hrs ofconditioning) may be necessary to ensure films with the best active coreproperty (longest life time and highest photoluminescence) aredeposited. Substrate 16 is then preheat at about 350° C. for about 30min before deposition.

The active core film was deposited onto a 6 inch thermal oxide wafer,which has been previously discussed, from the 1.5/0 target. The thermaloxide thickness was about 10 μm as described in previous examples. Theactive core is deposited to a thickness of about 1.2 μm with adeposition time of approximately 1 hr. The process condition are aslisted in Table 4 below.

TABLE 3 Target Pulsing Reverse Power Ar/O2 Frequency Bias pulsing (KW)(sccm) (KHz) (W) time (us) 6 60/28 120 100 2.3

A straight waveguide pattern can then be formed by a standardphotolithography procedure. The active core was etched using reactiveion etch followed by striping and cleaning. Finally, a 10 μm topcladding layer is deposited using a similar process. A target havingcomposition 92 cat. % Si and 8 cat. % Al with deposition parameters asdescribed in FIG. 9 was used to deposit the top cladding. The differencebetween the index of refraction between the core and the cladding isthen about 3.7%.

In this example, annealing of the amplifier structure was performed atvarious anneal temperatures. The results of the various anneals areshown graphically in FIGS. 27 and 28. FIG. 27 shows both internal gainin the C-band and insertion loss at 1310 nm of a 2.5 μm wide, 10.1 cmlong waveguide as deposited in this example as a function of annealingtemperature. The life time in ms and up-conversion constants in cm⁻³/smeasurements for the deposited active core film at different annealingtemperature are shown in FIG. 28.

EXAMPLE 5

One of the problems encountered during the reactive sputtering from analloy metallic target is that the film composition drifts from run torun due to the difference in sputtering yields from the elements thatforms the target alloy. For example, with Ar as a sputtering gas, thesputtering yield of Aluminum is about 3-4 times that of Silicon, whilesputtering yield of Alumina is only about 50% that of Silica. Therefore,during the metal burn in, more Aluminum is sputtered from the target,resulting in a Si rich target surface. When sputtering in the poisonmode, more Silica will be removed from target. Thus, as deposition goeson, the composition of the film deposited on substrate 16 will driftfrom lower Alumina concentration to higher Alumina concentration. Thisresults in the index of refraction of a film drifting up with subsequentdepositions from a target 12, as is shown for the deposition describedin Example 4 in FIG. 29. FIG. 30 shows the drift in photoluminescencepumped at 532 nm with subsequent depositions. FIG. 31 shows drift in theexcited state lifetime with subsequent depositions from a target. Theembodiment of target 12 utilized in FIGS. 29 through 31 is the 1.5/0target and the deposition parameters are as described above in Example4.

The drift can be stabilized by recondition target 12 prior todeposition. The recondition process (or burn in) consists of bothsputtering in metallic mode and then sputtering in poison mode tocondition target 12. The burn in time in metallic mode needs to be asshort as possible and at the same time insure no arcing during thepoison mode deposition. FIG. 32 shows the much improved drift in theindex of refraction and the photoluminescence when target 12 isreconditioned between subsequent depositions.

EXAMPLE 6

This example describes the fabrication of another Er—Yb codopedwaveguide amplifier according to the present invention. The active coreis deposited with an embodiment of target 12 with composition about 49cat. % Si, 48 cat. % Al, 1.6 cat. % Er and 0.5 cat. % Yb, which can befabricated as described in the '341 application. Target 12 was firstcleaned by sputtering with Ar (80 sccm) only in the metallic mode.Target 12 was then conditioned in poison mode by flowing 60 sccm ofArgon and 40 sccm of oxygen respectively. The pulsed DC power suppliedto target 12 was kept at 5 kW. Table 4 shows photoluminescence and indexof refraction of as-deposited films from this example at some typicalprocess conditions. The units for photoluminescence are the number ofcounts per micron. Lifetime and photo luminescence measured afterannealing at various different temperatures are shown in Table 5.

Target 4 Target Pulsing Reverse Power Ar/O2 Frequency Bias pulsing time532 nm (KW) (sccm) (KHz) (W) (us) PL/um Index 5 60/34 120 100 2.3 33671.5333 5 60/30 120 100 2.3 3719 1.5334

TABLE 5 Anneal Temperature ° C. Life Time (ms) PL (532 nm)/um 725 3 7000775 3 7000 800 4 7500 825 4.7 8560 850 5.8 10000 900 6.9 17000

A waveguide amplifier was fabricated using this material in the similarfashion as described in examples 2-4. The active core was firstdeposited on substrate 16, which includes a 10 um thermal oxide layer,using the following deposition parameters: target power 5 KW, pulsingfrequency 120 KHz, bias 100W, reverse time 2.3 us, Argon and Oxygen floware 60 sccm and 30 sccm respectively. The active core thickness isdeposited to a thickness about 0.2 μm, which takes approximately 1 hr.All wafers are preheated at about 350° C. for 30 min before deposition.A straight waveguide pattern is then formed by standard photolithographyprocedure. The active core was etched using reactive ion etch followingby striping and cleaning. Next, a 10 μm top cladding layer is depositedusing similar process. The “92/8” (92 cat. % Si and 8 cat. % Al)metallic target was used to deposit top clad according to depositionparameters shown in FIG. 9, resulting in a 4% index difference betweenactive core and cladding. The wave guide was then annealed at 800° C.for about 30 min.

This waveguide was tested for gain using the method described inprevious examples. However no net gain was observed from this waveguidesince the passive loss was too high.

EXAMPLE 7

In addition to active material layers (i.e., layers having rare-earthion concentrations), passive layers can also be deposited. FIG. 9 showsdeposition parameters for several target compositions, including sometargets for deposition of passive (i.e., alloys of Al and Si with norare earth ion concentration) layers. In this example, an embodiment oftarget 12 with a material composition of pure silicon is utilized.

Apparatus 10 can be based on an AKT 1600 reactor and deposited withabout 1 to 3 kW of pulsed DC target power supplied to target 12.Particular depositions have been accomplished at 2.5 kW and 1.5 kW. Thefrequency of the pulsed DC power is between about 100 and 200 Khz. Somedepositions were performed at 200 kHz while others were performed at 100kHz. The reverse time was varied between about 2 μs and about 4 μs withparticular depositions performed at 2.3 μs and 3.5 μs. The bias power tosubstrate 16 was set to zero.

Index variation of SiO2 films with bias to substrate 16 and depositionrates as a function of bias power to substrate 16 is shown in FIG. 10.

The process gas included a mixture of Ar, N₂ and O₂ The Ar flow rateswas set at 20 sccm while the O₂ flow rate was varied between about 5 andabout 20 sccm and the N₂ flow rate was varied from about 2 to about 35sccm. FIG. 33 shows the variation in the index of refraction of a filmdeposition on substrate 16 as the O₂/N₂ ratio is varied.

EXAMPLE 8

Alternatively, films can be deposited on substrate 16 from a purealumina target. In an example deposition with an embodiment of target 12of alumina in an embodiment of apparatus 10 based on the AKT 1600reactor, the pulsed DC target power was set at 3 kW and the frequencywas varied between about 60 kHz and 200 kHz. The reverse time was set at2.5 μs. Again, no bias power was supplied to substrate 16. The O₂ flowrate was varied from about 20 to about 35 sccm, with particulardepositions performed at 22 and 35 sccm. The Ar flow rate was set at 26sccm. A post deposition anneal of substrate 16 at 800° C. for 30 min.was performed.

FIG. 12 shows the variation of refractive index of the film deposited onsubstrate 16 with varying frequency of the pulsed DC power supplied totarget 12. FIG. 11 shows the variation in refractive index of a filmdeposited on substrate 16 with varying O₂/Ar ratio. As can be seen fromFIGS. 33, 34 and 35, the index of refraction of films deposited fromalumina can be adjusted by adjusting the process gas constituents or byadjusting the frequency of the pulsed DC power supplied to target 12during deposition.

EXAMPLE 9

Additionally, passive films can be deposited from targets having acomposition of Si and Al. For example, layers have been deposited fromembodiments of target 12 with composition 83% Si and 17% Al. About 4.5kW of pulsed DC power at about 200 kHz frequency was supplied to target12. The reverse time was about 2.2 μs. A bias power of about 150 W wassupplied to substrate 16 during deposition. FIGS. 14 and 15 showvariation of the index of refraction for subsequent runs from thistarget.

The examples and embodiments discussed above are exemplary only and arenot intended to be limiting. One skilled in the art can vary theprocesses specifically described here in various ways. Further, thetheories and discussions of mechanisms presented above are fordiscussion only. The invention disclosed herein is not intended to bebound by any particular theory set forth by the inventors to explain theresults obtained. As such, the invention is limited only by thefollowing claims.

1. A method of forming a waveguide amplifier, comprising: providing a substrate with an undercladding layer; providing an RF bias to the substrate; providing a target having a concentration of rare-earth ions opposite the substrate; supplying process gas between the target and the substrate; applying pulsed DC power where the voltage on the target oscillates between positive and negative voltages through a narrow band rejection filter that matches the RF bias to the target to deposit an optically active film; patterning the film to form a core; depositing an uppercladding layer over the core.
 2. The method of claim 1, wherein providing a substrate includes providing a silicon substrate with a thermal oxide layer.
 3. The method of claim 1, wherein providing a target includes providing a target having a concentration of up to about 5 cat. % of rare earth ions.
 4. The method of claim 3, wherein providing a target includes providing a target of Al and Si.
 5. The method of claim 1, wherein providing a target includes providing a target with a concentration of Al.
 6. The method of claim 5, wherein providing a target includes providing a target with a concentration of Si.
 7. The method of claim 5, wherein providing a target includes providing a target with a concentration of rare earth ions.
 8. The method of claim 1, further including providing bias power to the substrate.
 9. The method of claim 1, further including scanning a magnet over the target.
 10. The method of claim 1, wherein scanning the magnet over the target includes moving the magnet in a first direction.
 11. The method of claim 10, wherein the magnet extends beyond the target in a second direction perpendicular to the first direction.
 12. The method of claim 1, wherein the target has a surface area greater than the surface area of the substrate.
 13. The method of claim 8, wherein the filter rejects power at a frequency of the bias power. 